Photoelectric switching system



Jan. 13, 1959 G. L. HORWEGE ETAL 2,869,044

PHOTOELECTRIC SWITCHING SYSTEM Filed May 10, 1955 7'0 Courmuaao CIRCUITj E I r 63 E/V/V L. HOEWEGE UA/V/EL (A 77POJAK a (#424 55 W (/OBB/NSmmvrozes United States Patent PHOTOELECTRIC SWITCHING SYSTEM Glenn L.Horwege, Los Altos, Daniel T. Trojak, East Palo Alto, and Charles W.Jobbins, Menlo Park, Calif., assignors, by direct and mesne assignments,to said 'Glenn L. Horwege Application May 10, 1955, Serial No. 507,448 2Claims. (Cl. 317-130) This invention relates generally to aphotoelectric switching system, and more particularly to a photoelectricswitching system responsive to sudden changes in illumination.

There are 'many applications where it is necessary to have a switchoperate for a predetermined period of time. As an example, let usconsider a patrolman walking his beat. At each of the variousestablishments located on his beat, the patrolman walks to the window ordoor and shines his flashlight through the window and inspects theinterior. The illumination provided by the flashlight is low, and,consequently, many portions of.the interior cannot be seen. When aperson drives into his driveway at night, it is convenient to have theoutside lights turn on for a period of time while he walks to the dooror opens the garage. When guests arrive. at night, outside lighting isdesirable.

It may be inconvenient or undesirable to manually operate a switch. 7electric switching system in which the switch is operated by a suddenchange in illumination. For example, the patrolman would shine hisflashlight on the switching means and have it turn on the lightsautomatically. Similarly, the automobile headlights would operate theswitching means. The switching system should also include means wherebythe switch is turned otf after a predetermined period oftime. Thus, theinterior lights or the outside lights would be extinguished.

In the past, photoelectric switches have been employed to controlillumination. These switches have, in general, been responsive tochanges in the level of illumination and have served to turn on lightswhen the level of natural illumination has dropped to a predeterminedvalue, or to turn off lights when the level has reached a predeterminedlevel.

It is an-object of the present, invention to provide a novelphotoelectric switching system.

It is another object of the present invention to provide a photoelectricswitching system which is responsive to sudden changes in light.

It is another object of the present invention to provide a photoelectricswitching means which is operated by a sudden change in illumination andwhich remains in its operating position for a predetermined period oftime.

These and other objects of the invention will be more clearly apparentfrom the following drawings and description showing by way of example apreferred embodiment of the invention.

Referring to the drawings:

Figure 1 shows a perspective view of a switch housing including thephotosensitive device; and

Figure 2 is a circuit diagram of a photoelectric switching systemconstructed in accordance with our invention.

Referring particularly to Figure l, a housing 11 is shown which includesan aperture 12. The housing 11 serves to mount the electronic componentsand the photosensitive device 13. The photo-sensitive device may be Itis desirable to provide a photohi any suitable photoelectric device.vice 13 may be a phototube.

For purposes of illustration, the apparatus is shown connected to afloodlight 14 through the cable 16.

When the illumination falling on the photo-sensitive device 13, throughthe opening 12, is suddenly decreased, the switching means is operatedand remains in this position for a predetermined time. The circuit thenreturns to its normal position. Thus the floodlight is energized for apredetermined time. A power relay may be connected to the switchingsystem and serve to control associated power circuits.

In Figure 2, we have shown a switching circuit which can be employed tocarry out the invention which includes a phototube 21 and first andsecond amplifier tubes 22 and 23. A D.-C. supply voltage is connectedbetween lines 24 and 26. The phototube 21 is connected in series withresistor 27 across the lines 24 and 26. The point 28 is at a potentialwhich is determined by the value of the resistor 27 and thelight-impinging upon the phototube 21. The value of the resistor 27 ischosen such that the tube 22 is normally biased-beyond cut-off. Thecathode resistor 29 is connected to the cathodes of the amplifier tubes22 and 23. The plate of tube 22 is connected to line 24 through relaycoil 31. The relay 31 may be of the double pole type shown, or any otherrelay suitable for controlling associated circuits.

The grid of tube 22 is For example, the deconnected to line 26 throughthe grid leak resistor 33. The grid of tube 22 is also coupled to thepoint 28 through capacitor 34. Resistor 36 and capacitor 37 areconnected in series between the plate of tube 22 and the grid of tube23. Gne set of contacts 38 of the double pole switch is connectedbetween the common junction of resistor 36 and capacitor 37 and thecathodes of the tubes. The grid of tube 23 is resistively connected toline 24 through the series combination of fixed resistor 39 and variableresistor 41. The plate of tube 23 is connected to line 24 through plateresistance 42.

Operation of the circuit described is as follows: The grid of the tube23 is biased positively by the series combination of resistors 39 and 41connected to line 24. Under normal operating conditions, the tube 23 .isconducting a high plate current. Since tubes 22 and 23 have a commoncathode resistor 29, the grid of the tube 22 is biased beyond cut-01f.Thus tube 22 is nonconducting and tube 23 is conducting.

The action of capacitor 34 is to prevent slow changes in the photo'tubeillumination, such as those resulting from an accumulation of dirt onthe light source, aging of the light source, or changes in the generalbackground illumination, from causing the switching system to operate. Asudden decrease in the illumination on the phototube acts dilferently.When the illumination on phototube 21 is instantly decreased, thevoltage drop across the tube increases instantly. There is an equalvoltage rise across the resistor 33 since the voltage across thecapacitor 34 can not change instantaneously. As a result, the tube 22starts to conduct current. This energizes relay 32. When relay 32 isenergized, the contact 40 which controls the associated circuit and thecontact 38 are closed. Closing of the contact 38 applies a negativepotential to the grid of tube 23, thereby cutting off the tube. Thus,only tube 22 is conducting, and the bias across the resistor 29' due tocurrent flow through the tube 22 is not suflicient to cut it out. Thecapacitor 37 slowly discharges through the resistors 39 and 41 until thevoltage on the grid of tube 23 is raised sufi'iciently to cause the tubeto conduct. When tube 23 conducts, the bias across the resistor 29 issufiicient to cause the tube Patented Jan. 13, 1959.

Resistors:

27:12 meg S2 29:10009 33:3.9 meg S2 36:330 kilo Q 39:470 kilo S242:1000fl; and

4-1 was a 10 meg 9 variable resistor Capacitors:

C2=.005 microfarad; and

C3=4 microfarads Tubes 22 and 23 were a dual triode known bymanufacturers specifications as a 12AU7. Phototube 21 was of the typeknown by manufacturers specification as #935). The D-C. coil 31 of therelay had a resistance of 500032.

Apparatus constructed with the components specified above was tested andfound to be insensitive to changes in light varying from nighttime todaylight conditions. The photoelectric switching system was responsiveto sudden changes in illumination such as aiiorded by flashing lightfrom a flashlight on the phototube 21. The time during which the circuitoperated the relay could be varied between 2 and 70 seconds by varyingthe resistance 41.

it is apparent that if the positions of the phototube 211 and resistor27 are interchanged the tube 22 will become conductive when theillumination is suddenly increased. This might be desirable whenemploying the switch to turn. on lights in response to automobileheadlights.

Thus it is seen that we have provided a novel photoelectric switchingsystem which is operated by sudden changes in illumination and whichremains in its operating position for a controllable period of time.

We claim:

1. A photoelectric system comprising first and second voltage supplylines, first and second tubes, each having at least plate, grid andcathode elements, a relay means having a coil and plurality of contacts,said coil connected in the plate circuit of the first tube, seriallyconnected resistance and capacitance elements connected between theplate of the first tube and the grid of the second tube, resistancemeans connected between the grid of the second tube and the first supplyline serving to bias said tube whereby the same is normally conducting,a

resistor and photoeletcric means connected between the supply lines, acapacitor servingto couple the grid of the first tube to the commonjunction of the resistor and photoelectric means, said last resistorhaving a value whereby said first tube is normally non-conductive andsaid last capacitor serving to make said first tube insensitive togradual changes in illumination, one set of said relay contactsconnected between the cathode lead of said second tube and the gridcapacitor, said relay contacts closing to cut otf said second tube whenthe first tube is rendered conducting in response to a sudden change inillumination, said bias resistor and capacitor serving to form a delaycircuit which maintains the second tube cut-off for a predeterminedtime.

2. A photoelectric system comprising first and second voltage supplylines, first and second tubes each having at least cathode, grid andplate elements, a common cathode resistor connected in the cathode pathof said tubes and the second'voltage supply line, relay means having acoil and a plurality of contacts, said coil connected between the plateof the first tube and the first supply line, serially connectedresistance and capacitance elements connected between the plate of thefirst tube and the grid of the second tube, a variable resistanceconnected between the grid of the second tube and the first supply line,said resistor serving to bias the grid of said tube whereby the tube isnormally conducting, a serially connected photoelectric tube andresistor connected between said supply lines, a coupling capacitorserving-to couple the grid of the first tube to the common'junction ofthe serially connected resistance and photoelectric tube, said resistorbeing chosen whereby the first tube is biased to be non-conducting undernormal conditions of illumination, said capacitor serving to make saidtube insensitive to gradual changes in illumination but triggering saidtube into a conductive stage upon sudden changes in illumination, oneset of the relay contacts connected between the cathode lead of saidsecond tube and the common junction of the capacitor and resistorconnected to the grid, said contact closing when the first tube becomesconducting and serving to cut oif the second tube, said capacitor thendischarging through the grid resistor of the second tube, said tubebecoming conducting after a predetermined controllable time delay, saidsecond tube serving to conduct a high plate current whereby the firsttube is biased to cut off by the common cathode resistor.

References Cited in the file of this patent UNITED STATES PATENTS2,517,554 Frommer Aug. 8, 1950 2,547,332 Loveless et al Apr. 3, 19512,551,224 Spierer May 1, 1951 2,582,676 Bordewieck et al Jan. 15, 19522,718,612 Willis Sept. 20, 1955 2,802,155 Marsden Aug. 6, 1957

